Electronic circuits and devices may be DC or AC coupled to other circuits or devices. DC coupling allows both the AC and DC components of a signal to pass, while AC coupling uses a coupling capacitor to filter the DC component from a signal with both AC and DC components.
Certain circuits are designed to be selectively AC or DC coupled. However, the presence of a coupling capacitor in the circuit gives rise to parasitic effects when the circuit is DC coupled. Consequently, such circuits are typically designed to disconnect or short the coupling capacitor when DC coupled.
For integrated circuits, coupling capacitors are typically formed external to the integrated circuit—off-chip. A number of off-chip components are commonly used to disconnect or short the coupling capacitor.
As modern circuits become increasingly integrated, an improved approach which reduces the number of board components is desirable.